One of the components of a circuit that steps up or steps down voltage is a reactor. For example, Patent Literature 1 discloses a reactor that is used as a circuit component of a converter installed in a vehicle such as a hybrid vehicle. As shown in FIG. 10(A), a reactor 100 includes a coil 102 that has a pair of coil elements 102a and 102b being paralleled such that their respective axes are in parallel to each other, and an annular core unit 103 that has a pair of intermediate core portions 1030 around which the coil elements 102a and 102b are disposed. Note that, in FIG. 10(A), one coil element 102a is shown as being partially cut-out, such that the core pieces can clearly be seen.
The core unit 103 is structured with: a plurality of rectangular parallelepiped shaped intermediate core pieces 1031 that structure corresponding intermediate core portions 1030; a pair of U-shaped core pieces 103u disposed so as to clamp the opposite end faces of the intermediate core portions 1030 disposed in parallel to each other; and a plurality of gap members 103g each interposed between each ones of the core pieces for adjusting the inductance of the reactor 100. The U-shaped core pieces 103u are not provided with the coil 102 except for a pair of leg portions thereof connected to the intermediate core portions 1030, and are in an exposed state.